Oscar-nominated actor Will Smith stars in "Concussion," a dramatic thriller based on the true story of forensic neuropathologist Bennet Omalu, who made the first discovery of the football-related brain trauma, CTE. (  / Sony Pictures)

After a string of forgettable films (“After Earth,” “Focus”), Will Smith is back on his game with “Concussion,” snagging a Golden Globe nomination for his portrayal of real-life neuropathologist Bennet Omalu.

Omalu, a Ni­ger­ian immigrant, was an unknown Allegheny County, Pa., coroner until performing an autopsy on former Pittsburgh Steelers center Mike Webster, when he made a discovery that few wanted to hear. The injuries to Webster’s brain — corroborated by examination of other deceased football players, a disturbing number of whom had shown signs of early dementia and erratic behavior — suggested the existence of a new disease resulting from on-field head butting: chronic traumatic encephalopathy, or CTE.

The NFL had another acronym for Omalu’s conclusion: BS.

“Concussion” was adapted for the screen by director Peter Landesman (“Parkland”) from a buzzy GQ article by Jeanne Marie Laskas. Smartly, the drama opens not by focusing on the scientific, but on the emotional side of the story and the agonizing breakdown of “Iron Mike” Webster, who helped lead the Steelers to four Super Bowl victories in the 1970s. Toward the end of his life, as portrayed by David Morse, Webster was perpetually confused, living out of his pickup truck. His off-putting habits included applying Super Glue to his rotting teeth and using a taser on himself. He died, alone, in 2002.

While the media and masses are writing off the Hall of Famer as a sad, curious case of misspent fame and fortune, Smith’s Omalu decides to get to the bottom of Webster’s end-of-life spiral. Although the official cause of death is listed as a heart attack, Omalu orders more tests, paying for them himself. His findings reveal that Webster’s 50-year-old brain bears striking similarities to those of much older Alzheimer’s patients.

Almost as quickly as Omalu can publish his findings, the NFL sets about discrediting the doctor and his work. It’s all nonsense, according to spokesmen for the ­multibillion-dollar sports league. Just like that, a likeable, soft- spoken David has found his Goliath.

Will Smith as Dr. Bennet Omalu in “Concussion.” (Columbia Pictures)

Smith renders Omalu as a pious, if quirky, genius, one who talks to cadavers and decorates the rearview mirror of his Mercedes with a cross. His life revolves around his work, until he meets a Kenyan immigrant, Prema (Gugu Mbatha-Raw).

Prema’s presence in the film allows the character of Omalu to convey to the audience his newly conflicted feelings about America, which used to seem like an earthly paradise, he explains. But once the NFL begins to wage war on the doctor — enlisting football fans as foot soldiers, who ambush him with threatening phone calls — he’s not so sure about his adopted home.

As Omalu, Smith gives an emotional performance, bolstered by capable supporting players. Albert Brooks is especially good as Omalu’s wry boss and chief advocate, Cyril Wecht, lightening the film’s otherwise gloomy mood.

The themes in “Concussion” mirror those of another awards contender. In “Spotlight,” a relentless group of muckraking journalists takes on another powerful organization: the Catholic Church. If that drama proves anything, it’s that a great story doesn’t need to be overdramatized.

“Concussion,” on the other hand, is a little more heavy- ­handed, especially in its handling of the narrative of a put-upon immigrant losing faith in the American dream. That thread only serves to overshadow a far more troubling story: one about the NFL’s stop-at-nothing smear campaign and how easily the public bought into it.

PG-13. At area theaters. Contains some disturbing images and strong language. 123 minutes.